You make the mistake of viewing Marxist economic theory in a vacuum. The sort of oppresion that happened in the Soviet Union was not a by-product or coincidence that just happened to go with Marxist economic doctrine, it was the muscle that was needed to enforce Marxism. Don't confuse a welfare state with a communist police state. One may well lead to the other, but it doesn't have to (Example: Sweden), and it's not the same thing.
Although in a sense you're right. What we saw in the Soviet union was actually Stalinism. Still, I think the sentiments expressed in the article are overblown and self-pitying, and PC is alive and well anyway.
Your argument is fraught with bad logic.
Let me start with your main point.... You make the mistake of viewing Marxist economic theory in a vacuum.
That is the only way you can treat Marx, since his theory
is purely intellectual; having no practical application.